The present invention is related to a catalytic process and apparatus for the selective hydration of alkylene oxides.
The production of alkylene glycol, for example ethylene glycol, by thermal or catalytic hydration of the respective alkylene oxide is a well known reaction. Temperature, pressure, residence time, reactor design and the ratio of reactants are adjusted to optimize the thermal process. The catalytic processes add the nature of catalyst to the above mentioned process variables. A large number of catalysts have been used including anionic or cationic ion exchange resins. U.S. Pat. No. 4,937,393 discloses the use of sodium formate or trimethylamine acetate plus acetic acid as hydration catalyst. JP 61-271229 teaches the use of sodium glutamate. JP 61-271230 teaches the use of anthranilic acid as catalyst. U.S. Pat. No. 4,620,044 discloses the use of a bed of zeolite ZSM-5,H-form, as catalyst. U.S. Pat. No. 4,277,632 describes the use Mo or W metal or salts as catalysts. JP 54-128507 discloses the use of sodium tungstate, whereas U.S. Pat. No. 5,488,184 discloses the use of strongly basic ion exchange resin of the quaternary ammonium type, exchanged with bicarbonate as catalyst. Further, U.S. Pat. No. 4,165,440 teaches the use of fluorinated acid exchange resin deposited on a silica support as catalyst. U.S. Pat. No. 4,393,254 mentions the hydration catalyzed by partially amine-neutralised sulfonic acid resins. U.S. Pat. No. 5,260,495 discloses the use of hydrotalcite catalyst which contains Ni and Al, a large organic anion such as terephthalate and a metalate such as niobate or vanadate as catalyst. Finally, U.S. Pat. No. 5,064,804 and U.S. Pat. No. 4,967,018 disclose similar hydrotalcite catalysts.
Some of the prior art processes disclosed above show low selectivities and conversions, being sometimes even lower than the values reported for thermal processes. Further, other prior art references disclose very long contact times, i.e. low liquid hourly space velocity values (LHSV), which impose the use of high amounts of catalyst. Further, no reference discloses the pressure drops induced by such high volume of catalyst. In the prior art processes, an efficient dissipation of reaction heat and, implicitly, good temperature control over the reaction zone is complicated.
The hydration of alkylene oxide (for example ethylene oxide (EO)) is a highly exothermic reaction. The first reaction is a typical hydration while the consecutive ones are reactions of alkylation at oxygen of monoethylene glycol with ethylene oxide; the activation energy (Ea) for the hydration reaction is lower than that for the consecutive reactions, therefore a decrease of the reaction medium temperature will decrease the chance for consecutive reactions.
To avoid the consecutive alkoxylation reactions, it is also advisable to run the process with very short residence time still maintaining an almost total conversion of alkylene oxide. To fulfill this requirement, a highly active catalyst is required. The use of a highly or superactive catalyst enables one to run the process at lower temperatures, thus hampering those consecutive reactions with higher activation energies, which are generating side-products and are lowering the selectivity of the process. In the meantime, by employing such high or superactive catalysts, one can achieve almost total conversions at ultra short contact (residence) times.